Farming marine species

The Norwegian aquaculture industry is based primarily on producing the salmonid species Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss, native to the Pacific Ocean). Interest in farming of marine species first began to emerge in the 1980s, and has encountered environmental challenges not unlike those for salmonid production.

The key marine species have been Atlantic cod (Gadus morhua), Atlantic halibut (Hippoglossus hippoglossus), turbot (Psetta maxima) and spotted wolffish (Anarhichas minor) as well as the shellfish species blue mussels (Mytilus edulis), European flat oysters (Ostrea edulis L.) and king scallops (Pecten maximus).  

Norwegian waters provide an excellent natural environment for production of cod and halibut, and Norway’s knowledge about farming these species is at the international forefront. Many resources have been invested in developing cod and halibut farming, and the aquaculture industry and related R&D community have developed unique competencies. Nevertheless, cod production is in decline, (15 000 tonnes in 2011 in Norway), while halibut production remains at a low but stable level (3 000 tonnes in 2011). Norway has a national selective breeding programme for cod, but commercial progress has been hampered by the expanding production of whitefish species such as tilapia and striped catfish (Pangasianodon hypophthalmus) which compete with Norwegian whitefish products in certain markets. Moreover, wild stocks of cod appear to have recovered in Norway and are competing commercially with farmed cod products.

Production of spotted wolffish and turbot has gained very little footing in Norway (roughly 500 tonnes in 2011) and production of mussels, scallops and oysters remains small-scale as well. Although the market is potentially large, factors such as mussel shell quality, toxins that hinder mussel harvesting and high production costs still pose challenges.

One new development is the experimental production of cleanerfish that feed on sea lice off salmon in their cages. So far, wild-caught wrasses have been used to combat sea lice biologically at aquaculture facilities – but production of ballan wrasse (Labrus bergylta) and lumpfish (Cyclopterus lumpus) has begun.

The production of marine algae is another promising development. Currently in a testing phase for food production purposes, marine algae farming may find its largest application as a source of bioenergy.

Environmental impacts

Aquaculture facilities for marine species farmed in cages in coastal waters entail roughly the same kinds of environmental impacts as salmon production. These include:

  • Farmed fish individuals can escape (or spawn in cages) and go on to interbreed with and otherwise affect wild stocks of the same species.
  • Aquaculture activities require area in coastal waters and may therefore be competing for space with recreational activities, recreational fishing, commercial fishing and environmental conservation efforts.  
  • Parasites and disease can disperse to wild stocks; marine species can also spread these to salmon and sea trout.
  • Aquaculture facilities can disturb the habitats and breeding grounds of birds and other wildlife. Some bird species are attracted to aquaculture facilities, causing problems for producers. 


Cod have an exceptional ability to escape from sea cages, and do so far more successfully than salmon. Cod can also spawn in their cage, while salmon must be in fresh water to spawn. Interbreeding between farmed salmon and wild salmon stocks has been shown to have clear negative impacts. The Norwegian Environment Agency is concerned that escaped farmed cod, like escaped salmon, will have an impact on local, genetically distinct populations of coastal cod. As is the case with wild salmon, the local cod stocks have adapted to their habitat through natural selection over a very long time. If escaped farmed cod interbreed with local stocks of wild coastal cod, however, the wild fish could lose these genetic adaptations.

This could result in lower survival rates for the already weakened stocks of coastal cod. Clearly, it is essential to safeguard the genetic diversity among coastal cod so this important species can overcome pressures such as climate change and ocean acidification.

The conditions are ripe for farmed cod to interbreed with wild cod. Since 2006 the Institute of Marine Research (IMR) has been studying whether escaped farmed cod can influence the genetics of wild cod stocks in Norway’s fjords; findings so far have shown that cod eggs and larvae from in-cage spawning do spread to the natural environment. In 2009 it was documented that some of these survive to sexual maturity. In a larger fjord system, the researchers have also found larvae and fry originating from commercial cod farming. 

IMR has also succeeded in producing sterile (triploid) farmed cod, which could ultimately be a tool in minimising the ecological risk posed by escaped farmed cod. 

Threat from parasites, but there is hope to combat them

Norway has extensive experience with salmon farming and we know that the spread of parasites from aquaculture facilities to wild fish stocks is a major environmental problem. In the wild, marine species suffer a variety of parasites; 140 different parasites have been recorded for cod alone. It is still too early to tell which parasites will pose problems for future commercial cod farming.

The salmon louse (Lepeophtheirus salmonis) is a small crustacean that feeds on the mucous and skin cells of salmon. This parasite was present in nature long before salmon farming, but the sheer density of host animals available in aquaculture facilities provides ideal conditions for its rapid reproduction, growth and dispersal. Salmon lice, as eggs and in early-stage development, disperse into large areas of water around aquaculture facilities and attack wild salmon smolt en route from rivers to the open sea. It does not take many attacking salmon lice before a smolt dies of its wounds.

The problem of salmon lice (which do not attack cod) is a reference point from which to assess potential ecological problems related to parasites and the mutual impact between farmed and wild cod. But another species of sea lice, Caligus elongates, is also problematic in salmon farming and attacks cod as well – so this parasite could be harmful to both wild salmon and sea trout stocks, via both salmon farming and cod farming.

Cleanerfish, used to combat salmon lice biologically, can also be intensively produced. Two species in particular, the ballan wrasse and lumpfish, have passed the testing phase and are suitable for production. Wild catches of wrasse (mostly ballan wrasse and goldsinny wrasse) must be regulated sustainably, and wrasse mortality rates have been high in sea cages. The hardier lumpfish may be better suited for combatting sea lice farther north, where the wrasse are not indigenous.

Mussels attract eiders

At a mussel cultivation facility, wild mussels are simply allowed to attach to buoyed ropes placed out in a fjord. This is a good example of farming a localised species; the mussels are descendants of those found naturally on nearby rocks. The cultivated mussels are not fed, but rather filter plankton from the seawater.

Mussels are also the primary diet of the common eider, a sea duck which can consume a great many mussels from a facility. At the request of the Environment Agency, the Norwegian Institute for Nature Research (NINA) has studied conflicts between eiders and blue mussel cultivation (NINA Report 110).

According to the report:

  • There is no indication of any large-scale movement of eiders away from their natural habitat to feed on cultivated mussels; most of the mussel losses are due to facilities being placed in natural eider habitats.
  • Eiders inflict major losses, and in some cases mussel cultivation has been abandoned because the eiders made it unprofitable. Some producers have seen a flock of eiders eat (or knock off) an entire cultivated production within a short time.
  • When feeding at a facility, one eider consumes up to two kg of mussels per day, and in the process can knock as much as eight kg per day off the cultivation ropes. Once a flock has discovered a mussel facility, there appears to be no effective method to keep the eiders away.
  • Mussel facilities should not be placed in areas with eiders.

Only in exceptional cases is it acceptable for an industry to eliminate birds in order to prevent damages. Eiders are protected year-round along nearly the entire coast of Norway, and they have a special place in Norwegians’ hearts as a symbol of coastal nature. Poaching of this species is rare. It is not possible or effective to eliminate certain particularly damaging individuals either, since blue mussels comprise 95 % of the eider diet.

Macroalgae for food and energy

For centuries, a variety of seaweed and kelp species have provided food for people and feed for animals. Norway has a long history of research on and utilisation of these resources; the Norwegian alginate and seaweed-meal industry annually harvests roughly 200 000 tonnes of tangle kelp (Laminaria hyperborea) and the seaweed Ascophyllum nodosum.

The global application areas for these products include food, chemicals, medicine, cosmetics and fertiliser. The most recent focus is using seaweed for bioenergy production, driven by the demand for biomass towards sustainable production of biofuel, particularly for the transport sector. Seaweeds can contain up to 60 % carbohydrates, 80 % of which can be fermented to produce ethanol-36. Biofuels such as butanol and methane gas are also potential products.

Sugar kelp (Saccharina latissima) is the most promising species as a bioenergy resource, cultivated using artificial rafts and requiring no artificial fertiliser. Production is in its early stage, however, and developments on this front are still uncertain. But if sugar kelp is to be utilised on a scale to satisfy a portion of Europe’s need for alternative energy/bioenergy, then vast cultivation areas will be needed. It is still too early to assess the other environmental impacts of such activities.